1. Technical Field
This disclosure generally relates to a sealing assembly to seal an end of a rotator, such as an image carrier, used in an electrophotographic image forming apparatus, and to a developing device, a process unit, and an image forming apparatus incorporating the sealing assembly.
2. Description of the Related Art
In electrophotographic image forming apparatuses, such as printers, copiers, facsimile machines, and multifunction devices having two or more of copying, printing, and facsimile functions, a fine powder colorant called toner is typically used as developer. In such electrophotographic image forming apparatuses, an electrostatic latent image is formed on an image carrier, such as a photoconductive drum, the electrostatic latent image is developed as a toner image, the toner image is transferred onto a recording sheet, and the toner image thus transferred is fixed on the recording sheet under heat and pressure.
Such toner is stored in, for example, a toner container included in a development unit. A landscape-oriented opening is formed in a lower side surface of the toner container. A developing roller disposed in a transverse direction in the opening is rotated to move a thin layer of the toner held on an outer circumferential surface of the developing roller to a surface of the image carrier such as the photoconductive drum.
Sealing members are disposed at opposed ends of the developing roller or the photoconductive drum to prevent toner leakage. If toner leaks from between the sealing member and the developing roller, an inside of the image forming apparatus may be contaminated with toner, resulting in printing failures and further contamination of hands and/or clothes of an operator upon replacement of the developing device. Particularly, a nonmagnetic one-component developing device is likely to cause toner leakage.
For example, as described in JP-2003-056713-A, a sealing assembly may be disposed at each end of the developing roller or the photoconductive drum. As illustrated in FIG. 9A, such a sealing assembly has a sealing member 335 including felt or the like. A tip of a regulation blade 359 contacts a surface of a developing roller 358 inside the sealing member 335. The sealing member 335 is attached to a bearing surface 328 of a toner container 351 of a development unit. The bearing surface 328 includes an arc surface, a curved surface and a flat surface along the developing roller 358 and the regulation roller 359. It is to be noted that the regulation blade 359 is attached to the toner container 351 via a bracket 359a and a screw 359b. 
As illustrated in FIG. 9B, the sealing member 335 includes a sealing base 335c, such as felt or pile, having a predetermined thickness and attached onto an elastic member 335a such as sponge or rubber. A double-sided tape 335d is attached to a bottom surface of the elastic member 335a. The sealing member 335 of FIG. 9B is fixed to the bearing surface 328 of the toner container 351 with the double-sided tape 335d as illustrated in FIGS. 9C and 9D and an upper surface of the sealing base 335c contacts an outer circumferential surface of each end of the developing roller 358 under predetermined pressure, thereby preventing powder leakage. It is to be noted that a bearing hole 330 is provided to support a shaft of the developing roller 358 as illustrated in FIG. 9C.
However, such a sealing member cannot perfectly prevent powder leakage because, for example, polymerized toner or toner particles having a small diameter have been recently used in image forming apparatuses to achieve higher image quality. In order to maintain reliable sealing performance, the sealing member is pressed against the developing roller under higher pressure, or the sealing member has a relatively large thickness for full compression. As a result, larger heat is generated at the ends of the developing roller because of friction against the sealing member. In addition, an increased pressure force of the sealing member increases torque for rotatively driving the development unit, causing wear of a gear included in a power transmitting assembly and/or banding. Further, downsized and high-speed image forming apparatuses increase the rotation speed of the developing roller, causing larger heat to be generated at the ends of the developing roller by friction against the sealing member. Furthermore, polymerized toner having a low melting point has been recently used to achieve higher image quality and for energy saving. Such polymerized toner is likely to melt and adhere to the ends of the developing roller.
The toner melting and adhering to the end of the developing roller generates gaps among the developing roller, the sealing member and the regulation blade. A large amount of toner leaks through the gaps, causing imaging failures and contamination in the image forming apparatus. In addition, heat generated at the ends of the developing roller exposes the developing roller to high temperatures for a long time. As a result, the surface of the development may peel off and/or the developing roller may be broken.
As described above, a typical sealing assembly using only sealing pressure as a parameter is not enough to maintain reliable sealing performance while using polymerized toner having a low melting point to achieve higher image quality and for energy saving. A two-component developing device prevents toner and/or developer leakage by pressing a magnetic sealing member against a developing roller or a magnetic roller under low pressure. A one-component developing device needs a sealing member with a parameter other than pressure. Hence, a variety of techniques has been proposed to improve sealing performance without increasing a pressure force of the sealing member.
For example, JP-2001-154480-A proposes to prevent a gap from being created between both ends in an axial direction of a sealing member that seals shaft ends of a rotator and edges of a powder conveyance opening to prevent powder leakage.
JP2003-056713-A and JP2005-201427-A proposes use of a sealing member including hollow fiber to improve sealing performance and to reduce torque.
JP-2009-003308-A proposes use of an assisting sponge that absorbs a shearing stress to prevent deformation of a sealing member in a rotational direction caused by friction against a and prevent reduction in sealing performance, thereby preventing powder leakage.
JP2008-181047-A proposes use of different kinds of sealing members contacting a developing roller and a regulation roller, respectively, to improve sealing performance. Specifically, the developing roller contacts a sealing member that reduces sliding friction and the regulation blade contacts a sealing member that prevents powder leakage.
As described above, JP-2001-154480-A proposes to prevent a gap from being created between the sealing member and edges of the opening to prevent powder leakage. However, sealing performance between the sealing member and the rotator is not particularly considered. JP2003-056713-A and JP2005-201427-A proposes to improve sealing performance and to reduce torque by using the sealing member including hollow fiber. However, sealing performance at both ends in a circumferential direction may be insufficient. An object of JP-2009-3308-A is to maintain sealing performance by preventing deformation of the sealing member. Sealing performance between the sealing member and the rotator is not particularly considered. An object of JP2008-181047-A is to improve sealing performance of the regulation blade and sliding properties of the developing roller. Sealing performance for the developing roller is not particularly considered.